The Prime Minister has promised to move towards legalising same-sex marriage in the first 100 days of a re-elected Labor government, in the first - and perhaps last - leader's debate of the election campaign.

The exchange between Kevin Rudd and Opposition Leader Tony Abbott otherwise focused heavily on the economy and who could be trusted to best manage it.

The two leaders opened with lines from their stump speeches - Mr Rudd promising Australians "a new way" and Mr Abbott offering to "restore hope, reward and opportunity".

Key points

Debate focused heavily on the economy and who can be trusted to best manage it

Alongside the weighty discussion about the economy - in particular, productivity, costings and the GST - the issues of aged care, climate change, asylum seekers, Sydney's second airport and same-sex marriage were also addressed.

On the last point, Mr Rudd promised to allow a conscience vote in parliament on legislation before the end of the year.

"Within the first 100 days of a re-elected government, a bill would come forth to legalise marriage equality," he said.

"We would, of course on our side of politics, allow a full conscience vote and I would just appeal to Mr Abbott to do the same because folk out there want this to happen."

Mr Abbott said it was an "important issue", noting his sister Christine, who is gay, was in the audience at the National Press Club.

But he said the Coalition's priority would be "on things like reducing cost-of-living pressure and increasing job security" and would not commit to allowing a conscience vote.

"If this issue were to come up again in the future it would be a matter for a future party room," he said.

Mr Rudd had previously opposed changing Australia's marriage laws but announced earlier this year that he had reversed his position.

Economy dominated opening exchanges

Both leaders promised to build a stronger economy, with Mr Rudd emphasising Labor's record in handling the global financial crisis and saving jobs and its ability to handle the new challenges presented by the end of the mining boom.

"We need a new way to take Australia forward because of the new challenges we face," he said, pointing to Labor's National Broadband Network and its $15 billion school funding plan as factors which will boost productivity.

Each reprised old lines of attack on the other, with the Opposition Leader citing "pink batts that caught fire in people's roofs", and the Prime Minister pointing to Mr Abbott's previous comments on climate change, saying "we've never doubted the science - unlike some".

Mr Abbott also hit out at Labor over its border protection policies and Mr Rudd's decision last time he was Prime Minister to dismantle the Howard government's offshore processing regime.

"Mr Rudd closed it all down and it's because Mr Rudd closed it all down that we've had more than 50,000 illegal arrivals, more than 800 boats," he said.

However, Mr Rudd said he abandoned the Coalition's Pacific Solution because voters wanted him to.

"We had a mandate, we implemented that mandate and then our external circumstances, as you know, during the course of 2008, '09 and '10 changed," he said.

"There were many things that happened in the international community, including a civil war in Sri Lanka, so what I have said on many times already is with the benefit of 20-20 hindsight you would have begun to adjust the policy earlier."

Coalition claims win; Rudd performed 'beautifully'

On Sydney's second airport, the Opposition Leader promised to make a decision about the location within the first term of a Coalition government.

But Mr Rudd failed to repeat his Deputy's promise made last month to start building the second airport within the next term if Labor is re-elected.

"I'm from Queensland, not from Sydney," Mr Rudd said.

"I'll defer that question to, for example, Minister Albanese, the deputy Prime Minister, Minister for Transport, because that is how it's appropriately deliberated upon."

What they said: The key issues

Less than 10 minutes after the debate had ended, the Coalition campaign headquarters put out a release declaring its man had won the night.

Mr Abbott said "it was a great opportunity to present some plans to the Australian people", but said he wanted more debates where the "people of Australia" could ask the questions.

Mr Rudd said "it was for the Australian people to decide" how well - or not - he had performed.

As she was leaving the venue, Mr Rudd's wife, Therese Rein, said her husband had done "beautifully".

Viewers of the major television networks were divided on who they believed had won - Channel Seven, Sky News and the respected Laurie Oakes gave it to Mr Abbott; the ABC and the Nine and Ten networks gave it to the Prime Minister.

Rudd accused of 'cheating'

Some of the post-debate debate centred on Mr Rudd's use of notes which the Coalition says breached the agreed rules.

Shadow finance minister Andrew Robb was blunt in his assessment:

"I think Mr Rudd has said that the whole election is based on trust, and the very first thing he did was to cheat. He broke the agreed rules about no notes," he told ABC News 24.

"I think Tony Abbott looked like a leader and Kevin Rudd looked like a reader."

Mr Rudd's office said there was "absolutely no intention to do anything other than comply with the rules".

"The PM arrived at lectern in full view of the audience and the panel. There were no objections raised at any time," a spokesperson for Mr Rudd said.

"We have always believed this rule is aimed at preventing the use of props.

"The PM is happy to debate Mr Abbott at any time during the election campaign without notes."

Free trade is the oldest argument in federal politics and the issue that literally defined the federation era but opposition exists to the TPP, courtesy of the Investor-State Dispute Resolutions clause.